Now it won't run?
'99 Chevy, same as my '01 GMC. Everything is on the right side for heat and air.
On the way home from Mammoth Springs a couple of years ago I could smell anti freeze in the cab. I looked at utube videos on how to change the heater core. My son and I changed it out in about 4 hours along with cabin air filter and all the O rings needed for about $150. Wish I had seen the video of cutting the slot in the cabinet to change the filter without pulling the whole unit before hand, not after it was reinstalled. Bad design for a filter that needs to be changed every couple of years.
Going to different shops to have the ac pumped down, checked and freon added I found prices from $40 to $260.